1. Field of the Invention
The invention relates to a configuration of a speaker voice-coil bobbin and a method of manufacturing the speaker voice coil bobbin.
The present application claims priority from Japanese Application No. 2001-103118, the disclosure of which is incorporated herein by reference for all purposes.
2. Description of the Related Art
Conventionally, as a base material for forming a bobbin on which a voice coil of a speaker is wound, a paper material such as kraft paper, a heat-resistant resin film made of polyimide, polyamide or the like, metal foil made of aluminum or the like, and other such materials are employed.
The reason why paper material is employed as the base material of the speaker voice-coil bobbin is because of its light weight and low cost. However, the voice-coil bobbin formed from the paper material has the problem that it is flammable due to its low heat resistance and has inferior heat-dissipation properties.
Accordingly, when an abnormal current flows through the speaker or when abnormal heating occurs on the periphery of the speaker, there may be cases where an accidental fire originates in the voice-coil bobbin and spreads.
In addition, the voice-coil bobbin formed of the paper material is of inferior humidity resistance and water resistance. The absorption of water or moisture by the paper material causes degradation in the binding between the fibers, resulting in a decrease in strength.
Therefore, the paper-material-made voice-coil bobbin has a problem that it is unfit for speakers placed in harsh use-environments where water may be directly poured on the speaker or in humid surroundings, e.g., a vehicle-mounted speaker.
The paper material also has the disadvantage of low rigidity.
The heat-resistant resin film made of polyimide, polyamide or the like is employed in order to solve the problems associated with the paper material, but it has the different problems of high cost, inferior adhesion properties and dissolution at high temperatures.
The voice-coil bobbin employing metal foil made of aluminum or the like in order to solve the problems associated with the paper material has high heat resistance, but also high specific gravity as compared with that of the paper material and the resin, and high thermal conductivity. Hence, heat generated in the voice coil is propagated through the entire bobbin, which causes the possibility of the melting or ignition of an adhesive for fixing the parts attached to the voice coil, such as a diaphragm, center cap and damper, and also fixing the parts to each other. As a result, the use of such a metal foil is attended with the problem that the materials for the parts and the like need to have high heat resistance.